Contents lists available at ScienceDirect Ceramics International journal homepage: www.elsevier.com/locate/ceramint Effect of suspension stability on bonding strength and electrochemical behavior of electrophoretically deposited HA–YSZ nanostructured composite coatings Hamidreza Farnoush ⁎ , Zohreh Rezaei Department of Metallurgy and Materials Engineering, Faculty of Engineering, University of Kashan, P.O. Box 87317-51167, Kashan, Iran ARTICLE INFO Keywords: Suspensions Nanocomposites Mechanical properties Electrophoretic deposition ABSTRACT In the present study, HA–YSZ nanostructured composites were deposited on Ti–6Al–4 V substrates by electrophoretic deposition of suspensions containing 0, 10, 20 and 40 wt% YSZ. The stability of each suspension was determined by applying response surface methodology, DLVO theory and zeta potential measurement for different YSZ contents and dispersant concentrations. The maximum zeta potential and electromobility of suspended particles was obtained for the suspension with 20 wt% YSZ. The electrophoretic deposition of HA– YSZ nanostructured composites was carried out at a constant voltage of 20 V for 120 s. The deposition kinetics was studied based on a mass-charge correlating approach under ranges of voltage (20–60 V), time (30–300 s) and wt% YSZ (0–40). The as–deposited and sintered HA–YSZ coatings were characterized by SEM, XRD, DSC– TG and FT–IR analyses. The micro-scratch behavior of coated samples indicated the highest critical contact pressures of crack initiation, P c1 = 4.50 GPa, crack delamination, P c2 = 5.14 GPa and fracture toughness, K IC = 0.622 MPa m 1/2 for HA-20 wt% YSZ sample. The results of potentiodynamic polarization measurements showed that the implementation of 20 wt% YSZ could efficiently decrease the corrosion current density and corrosion rate of coated samples, while corrosion potential and linear polarization resistance were increased. 1. Introduction Titanium and its alloys have special importance in biomedical implants, owing to their good biocompatibility, low density, low elastic modulus and excellent corrosion resistance [1]. However, the surface modification of Ti by bioactive ceramics coatings has received special attention due to the bio-inert surface and weak osteo-conductivity of titanium [2,3]. Hydroxyapatite (HA, Ca 10 (PO 4 ) 6 (OH) 2 ) is a known biocompatible and bioactive ceramic material, which is the best candidate for substitution in dental and orthopedic application due to its chemical and microstructural similarity to human bone tissues [4]. Despite these advantages, the extensive application of HA is restricted in load bearing areas due to the lack of sufficient mechanical strength and fracture toughness [4]. On the other hand, the bio-inert ceramic such as yttria stabilized zirconia (YSZ) can improve the toughness and strength of HA phase due to its superior mechanical properties [5]. Therefore, a coating with both biocompatibility and suitable mechanical properties is achieved by the deposition of HA-YSZ composite on metallic substrates. Electrophoretic deposition (EPD) is one of the most efficient surface modification techniques, which offers the possibility of generating homogeneous HA coating on Ti substrate [6,7]. Being economical, controlling the thickness and uniformity of coating, owing to simple equipment and short formation time [8,9], make the EPD process more favorable technique in comparison to other techniques like plasma spraying [10,11], sol-gel [12,13], bio- mimetic [14,15], ion implantation [16,17], micro-arc oxidation [18,19] and so forth. The EPD process is defined as a movement of suspended colloidal particles in a liquid medium under the influence of electric field and deposition on an oppositely charged electrode [8]. Nevertheless, the HA coatings deposited by EPD, suffers from the low bonding strength between the coating and substrate, the inade- quate densification of HA coatings after low temperature sintering and the thermal decomposition of HA into tricalcium (TCP) and tetra- calcium phosphates (TTCP) [8]. The degradation of metallic substrate and HA decomposition can be prevented by setting the sintering temperatures below 1000 0 C [20]. Moreover, the non-negligible difference between thermal expansion coefficients (CTE) of Ti-6Al-4V substrate (α Ti-6Al-4V = 8.9 × 10 -6 K -1 ) and HA coating (α HA = 14–16 × 10 -6 K -1 ) leads to high thermal tensile stresses at the substrate-coating interface which results in micro-crack formation during sintering and http://dx.doi.org/10.1016/j.ceramint.2017.06.036 Received 7 December 2016; Received in revised form 4 June 2017; Accepted 5 June 2017 ⁎ Corresponding author. E-mail address: farnoush@aut.ac.ir (H. Farnoush). Ceramics International xxx (xxxx) xxx–xxx 0272-8842/ © 2017 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Please cite this article as: Farnoush, H., Ceramics International (2017), http://dx.doi.org/10.1016/j.ceramint.2017.06.036